1. Field of the Invention
The present invention relates to an ionization smoke detector for detecting smoke produced due to a fire or the like.
2. Description of Related Art
An ionization smoke detector is generally known as a type of fire detector.
The above conventional ionization smoke detector comprises, for example, a base secured to a ceiling or the like, a detector body removably set to the bottom of the base, and an outer cover for covering the face (bottom) opposite to the base of the detector body.
The detector body comprises a circuit part comprising a printed circuit board on which electronic parts serving as a fire detecting circuit are mounted, a detecting part serving as a sensor for detecting smoke, and a body to which the circuit part and the detecting part are secured and which is removably set to the base.
Furthermore, the detecting part has, for example, an inner electrode having a radiation source, an intermediate electrode set so as to face the inner electrode, and an outer electrode (outer chamber) formed so as to cover the opposite side to the inner electrode of the intermediate electrode, in which the gap between the inner electrode and the intermediate electrode is formed as an almost-closed inner ionization chamber and the gap between the intermediate electrode and the outer chamber is formed as an outer ionization chamber allowing smoke to enter from the outside.
An opening is formed on the intermediate electrode so that the radiation emitted from the radiation source provided for the inner electrode can be also irradiated to the outer ionization chamber.
The ionization smoke detector uses a field effect transistor (hereafter referred to as FET) for detecting a potential change at the joint between the inner and outer ionization chambers and the intermediate electrode is connected to the FET.
Because an ionization smoke detector has a relatively complicate structure having an inner ionization chamber and an outer ionization chamber as described above, the detector has problems that it takes a lot of time to assemble and set the detector and it is difficult to decrease the cost.
For example, in the case of the FET, the insulation between terminals may be deteriorated due to humidity or dust. Therefore, it is preferable to use the FET in a closed state. Moreover, it is necessary that an intermediate electrode connected to the FET is set so as to face an inner electrode under an insulated state. Therefore, it is troublesome to set the FET and intermediate electrode.
The outer chamber is joined to the body by, for example, a plurality of screws. Therefore, the number of screws required to assemble an ionization smoke detector increases and thus, it is troublesome to set an outer chamber.
Further, in the case of an ionization smoke detector, it is necessary to remove the body from the base or the outer cover from the body. Therefore, the cover is set to the body and the body is removably set to the base.
In the case of the structure, when setting the body with the outer cover set on it to the base to assemble an ionization smoke detector, the outer cover set to the body may be removed and thus, the assembling operation is made complex.